1. Field
This invention relates generally to the storage, transportation and/or disposal of highly radioactive components, and more particularly, to a method of reducing the volume of radioactive boiling water reactor control rods for long term storage.
2. Related Art
One type of commonly used boiling water nuclear reactor employs a nuclear fuel assembly comprised of fuel rods surrounded by a fuel channel. Each fuel channel of a boiling water reactor fuel assembly typically consists of a hollow, linear, elongated, four-sided channel of integral construction, which, except for its rounded corner edges, has a substantially square cross section. Commonly, each channel is roughly 14 feet (4.27 m) long by five inches (12.7 cm) square and laterally encloses a plurality of elongated fuel elements. The fuel elements are arranged to allow for the insertion of a cruciform-shaped control rod, which, during reactor operation, is movable vertically to control the nuclear reaction. As is generally known, the control rods include an upper portion having a handle and four upper ball rollers for guiding the control rod as it moves vertically and a lower portion comprising a lower casting and lower ball rollers. The main body structure includes four blades or panels which extend radially from a central spline. Preferably, the blades extend longitudinally to a height that substantially equals the height of the fuel elements, which is approximately 12 feet (3.66 m). The width of the control rods at the blade section is approximately twice the width of the panels, which is in the order of 10 inches (25.4 cms.) and the blades are approximately 2.8 in. (7 mm.) thick.
Following functional service, boiling water reactor control rod blades are difficult to store and dispose of because of their size, configuration, embrittled condition, and radiological activity. Heretofore within the United States, in-pool storage of control rod blades has been extremely space inefficient and dry cask storage is not readily available.
Control rod blades and other irradiated hardware are typically Class C, low level radioactive waste as defined and determined pursuant to 10 CFR 61 and related regulatory guidance, e.g., NRC's Branch Technical Position on Concentration Averaging and Encapsulation. Since Jul. 1, 2008, low level radioactive waste generators within the United States that are located outside of the Atlantic Compact (Connecticut, New Jersey and South Carolina) have not had access to Class B or Class C, low level radioactive waste disposal capacity. Lack of disposal capacity has caused boiling water reactor operators considerable spent fuel pool overcrowding. Though currently very uncertain and subject to numerous regulatory and commercial challenges, Class B and Class C low level radioactive waste disposal capacity for the remainder of the United States low level radioactive waste generators is anticipated in the relatively near future.
One technique for reducing the volume of boiling water reactor control rods for spent fuel pool storage has been to sever the upper and lower portions of the control rods from the control rods' blades. In the remaining main blade structure, the individual blade sections have been removed from the central spline by longitudinal cuts and the severed parts are then stacked for storage or burial as described in U.S. Pat. No. 4,507,840. An alternate approach has been taken in U.S. Pat. No. 5,055,236, which suggests that the vertical cut be made along the center line of the spline to divide the control rod blades into two chevrons. The chevrons can then be closely stacked for storage. Each of the approaches yields twelve-foot (3.66 m) long segments that are costly to shield and transport. U.S. Pat. No. 4,507,840 recognizes that since the blades enclose neutron absorber rods which contain radioactive gas, the vertical cuts must be made quite near the central spline to avoid releasing the radioactive gases. Thus, horizontal segmentation of the blades, which would cut across the sealed rods that contain the neutron absorber material and the radioactive gases, is problematic.
Therefore, for safe shipment, a new method is desired for reducing the storage volume of a boiling water reactor control rod.
Furthermore, such a method is desired that will reduce the length and width of the segments to be transported so that they will fit in existing, standard, licensed transport casks.
Additionally, such a method is desired that will minimize the release of radioactive debris.